Maintaining a thriving reef tank requires more than just strong lighting and stable salinity—it depends on the precise balance of calcium and alkalinity. Corals, especially stony types like SPS and LPS, need these elements to build their skeletal structures and support metabolic function. This is where Seachem Reef Fusion 1 & 2 shine: a simple, two-part dosing system that delivers both calcium and carbonate alkalinity in perfect proportion.
In this complete guide, you’ll learn how Reef Fusion 1 and 2 work, how to dose them properly, and how to integrate them into your reef care routine for strong coral growth and vibrant coloration.
What Are Reef Fusion 1 and 2?
Reef Fusion is Seachem’s two-part supplement system designed to simplify calcium and alkalinity dosing in saltwater aquariums.
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Reef Fusion 1 provides calcium (100,000 mg/L) along with magnesium, strontium, boron, and other elements that enhance coral health.
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Reef Fusion 2 supplies carbonate and bicarbonate, which raise and stabilize alkalinity, essential for coral calcification and buffering pH.
Both parts are formulated to be used in equal volumes, ensuring balanced supplementation without the risk of major ionic imbalance that comes with single-solution dosing.
Why Are Calcium and Alkalinity So Important?
Corals extract calcium and carbonate ions from the water to form aragonite, the mineral that makes up their skeletons. Without enough of either, coral growth slows, tissue recession may begin, and colours fade.
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Low calcium leads to soft, incomplete skeletal development.
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Low alkalinity causes unstable pH and weak buffering, making corals prone to stress and bleaching.
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Imbalance between the two can result in precipitation and poor uptake.
Reef Fusion makes it easy to keep both values in check without advanced chemistry knowledge.
How to Test Before You Dose
Before starting any dosing routine, always test your current calcium and alkalinity levels. Use reliable test kits or digital meters:
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Ideal calcium range: 400–450 ppm
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Ideal alkalinity range: 8–11 dKH
Record your baseline levels and re-test frequently until the system stabilizes. In reef tanks with fast-growing corals, test at least twice a week.
How to Dose Reef Fusion 1 & 2
Step 1: Shake both bottles thoroughly
These solutions contain trace elements and minerals that may settle over time. Always shake well before dosing.
Step 2: Start with Seachem’s recommended dose
Seachem suggests 1 mL of Reef Fusion 1 and 1 mL of Reef Fusion 2 per 25 litres of tank water, dosed daily. This is a starting point, not a fixed dose.
Step 3: Dose equal parts of each component
If you add 5 mL of Reef Fusion 1, you must add 5 mL of Reef Fusion 2. Dose them at different times of day, ideally spaced out by several hours, to prevent precipitation and promote better absorption.
Step 4: Adjust based on test results
If your calcium or alkalinity is consistently low, gradually increase your daily dose by 25%, retest, and fine-tune from there. Never adjust both significantly on the same day.
Tips for Effective Reef Fusion Dosing
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Dose into a high-flow area of your sump or display to aid mixing.
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Avoid combining Reef Fusion with other calcium or alkalinity products unless specifically advised.
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Turn off protein skimmers for 30 minutes if you’re seeing microbubbles or residue immediately after dosing.
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If precipitation occurs (white dust in water or clogged equipment), recheck alkalinity and space out the dosing intervals further.
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Monitor magnesium monthly to ensure it remains in the 1250–1350 ppm range, as it affects calcium stability.
Can You Automate Reef Fusion Dosing?
Yes. Reef Fusion can be added to dosing reservoirs and delivered by dosing pumps, though you’ll need separate containers and lines for Part 1 and Part 2. Program your pump to dose each part several hours apart to avoid chemical interaction. Many reefers automate calcium and alkalinity this way for stable daily maintenance.
What If Calcium and Alkalinity Are Out of Balance?
If calcium is high and alkalinity is low, or vice versa, pause both and adjust only the deficient parameter for a few days using a single additive (e.g., Seachem Reef Builder or Reef Calcium). Once levels are aligned, resume 1:1 Reef Fusion dosing.
This targeted approach prevents wild swings and ensures your corals receive what they need without risk.
Is Reef Fusion Safe for All Reef Inhabitants?
Yes. Reef Fusion 1 and 2 are reef-safe, fish-safe, and invertebrate-safe. They contain no phosphate, nitrate, or harmful byproducts and are ideal for mixed reef tanks, SPS-dominant systems, and beginner setups alike.
When to Expect Results
With consistent use and correct adjustment, most reef keepers see:
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Improved polyp extension within a few days
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Noticeable skeletal growth in 1–2 weeks
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Brighter coral colours due to improved nutrient uptake
Final Thoughts: Stable Reef Chemistry Made Simple
Seachem Reef Fusion 1 and 2 provide an efficient, accessible way to maintain calcium and alkalinity in marine aquariums. Whether you’re managing a nano reef or a full SPS system, this two-part dosing system gives you reliable control over the elements your corals need to thrive.
By testing regularly, dosing with precision, and adjusting based on consumption, you can build a reef that’s colourful, stable, and continuously growing.
